A metal surface heat treatment apparatus and method

Abstract

The application discloses a metal surface heat treatment device and a treatment method. The device comprises a heat treatment equipment shell, an electric heating guide wire in the shell, a gas suspension rotating support system, a telescopic rotating driving system and a cooling and gas source pretreatment system. The gas suspension rotating support system uses a hollow suspension shaft with a suspension gas jet to non-contact lift the metal pipe by using low-temperature high-pressure gas pre-cooled by a heat exchange coil. The telescopic rotating driving system drives the suspension metal pipe to rotate by magnetic coupling. The cooling system cools the passing gas by cooling water in the heat exchange frame. The treatment method comprises the steps of loading, starting gas floating and heating, driving rotation, implementing heat-cold circulation and cooling and unloading. The application realizes non-contact and uniform heat treatment of the metal pipe at high temperature, solves the problem of magnetic suspension high-temperature magnetic loss and significantly improves the surface performance of the metal pipe by actively controlling heat-cold circulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal surface heat treatment, in particular to a metal surface heat treatment device and method. BACKGROUND

[0002] Metal surface heat treatment is a key process that changes the surface layer structure of a workpiece by heating, holding and cooling, without changing its composition, to obtain the required surface properties (such as high hardness, wear resistance) while maintaining the toughness of the core. For key components such as pipes and shafts, surface quenching and other treatments can significantly improve their wear resistance, fatigue strength and service life, and are widely used in mechanical manufacturing, automotive, aerospace and other fields.

[0003] Traditional surface heat treatment of pipe and shaft parts usually adopts induction heating, flame heating or box furnace heating followed by quenching. In these methods, the clamping and fixing of the workpiece is the first step. However, mechanical clamping inevitably brings a series of problems: first, the heat transfer conditions at the clamping site (usually the contact point of the chuck or clamp) are different from other parts, leading to uneven heating in this area, which is prone to soft spots or insufficient hardness, affecting performance consistency; second, for precision workpieces that have undergone surface coating treatment (such as protective coating or pre-coated catalytic layer), mechanical clamping force can easily cause coating indentation, scratching or even peeling, resulting in workpiece scrap; third, at high temperatures, the clamp itself may also deform, further affecting clamping precision and heat treatment effect.

[0004] To avoid the problems brought by clamping, some improvement schemes have been proposed in existing technologies. For example, the patent with publication number CN113621781B provides a device for gap-type feeding of metal pipes through non-clamping, which uses the friction between the heating block and the damping block to generate heat as an auxiliary heat source. However, this scheme has obvious limitations: there are physical gaps between multiple independent heating blocks, leading to uneven heating of the metal pipe and making it difficult to obtain uniform organizational properties; it relies on friction-generated heat, which is inefficient and has poor heat controllability, and more seriously, the friction process itself can cause wear and damage to the workpiece surface, especially precision coatings, which goes against the original intention of non-contact processing.

[0005] Another type of solution attempts to use non-contact support. For example, patent CN118006881A proposes the concept of using magnetic force to suspend metal pipes. This avoids physical contact, but introduces a more fatal defect: permanent magnets will demagnetize at high temperatures (Curie point effect), and when the temperature exceeds its Curie temperature, the magnetism will decrease sharply or even disappear completely. Surface heat treatment processes such as normalizing and quenching usually require austenitizing temperatures of 700°C to 900°C or even higher, far exceeding the Curie point of most high-performance permanent magnets (such as neodymium iron boron), which is usually between 310°C and 400°C. Therefore, this solution will inevitably fail to suspend due to demagnetization of the magnets during high-temperature processing, causing the workpiece to fall, posing a serious safety risk and quality risk, and greatly reducing its practicality.

[0006] In summary, the existing technology faces a dilemma when performing surface heat treatment on pipe and shaft parts: mechanical clamping can cause uneven heating, coating damage, and deformation; and the non-contact magnetic suspension solution cannot work stably in a high-temperature environment. In addition, most existing technologies focus on the heating method itself, lack effective means for dynamic and uniform heating of the workpiece during the heat treatment process, and do not utilize the cooling medium as an active process control factor to further improve the final performance.

[0007] Therefore, there is an urgent need in the art to develop a new type of surface heat treatment device and method that must be able to: 1) achieve stable, non-contact support of the workpiece at high temperatures, completely avoiding clamping damage and demagnetization risks; 2) ensure uniform heating of the workpiece during the heat treatment process, eliminating soft spots and uneven microstructures; 3) actively and accurately control the heat treatment process, especially the cooling stage, in order to achieve superior material performance. Such technology will greatly improve the manufacturing level of high-end metal parts. SUMMARY

[0008] The purpose of the present invention is to overcome the three major technical bottlenecks in existing surface heat treatment technology for metal pipe / axle parts: 1) uneven heating, coating damage, and workpiece deformation caused by mechanical clamping; 2) reliability issues of the non-contact magnetic suspension solution due to demagnetization of the magnets at high temperatures; 3) single means of heat treatment process control, which cannot actively intervene in the cooling process to optimize material microstructure and performance.

[0009] Based on this, the present invention proposes a completely new technical solution, the specific purposes of which include:

[0010] A non-contact support system based on the principle of air flotation is provided to ensure that the workpiece is in a stable suspended state throughout the high-temperature heat treatment process, fundamentally avoiding any form of mechanical contact damage.

[0011] An integrated rotary drive mechanism enables the workpiece in the suspended state to rotate at a uniform speed, thereby achieving uniform heating in the circumferential and axial directions, eliminating heat treatment soft spots, and improving the consistency of the microstructure.

[0012] A kind of active controllable cooling airflow system is designed, and the introduction of cooling medium is upgraded from simple protection function to an active process control means, to realize "heat-cold cycle" processing by accurate regulation, thereby refining grain and improving the comprehensive mechanical properties of workpiece.

[0013] Finally, a complete solution for surface heat treatment of precision workpieces in atmospheric environment is provided.

[0014] To achieve the above object, the present application provides the following technical solution: a metal surface heat treatment device, comprising a heat treatment equipment shell, an electric heating guide wire is installed on the inner wall thereof; further comprising:

[0015] Air-suspended rotary support system: including a vertical shaft fixed to the left inner wall of the heat treatment equipment shell, a rotating sleeve assembled on the vertical shaft, and a hollow suspension shaft with its left end fixedly connected to the rotating sleeve and its interior communicating with the rotating sleeve; The top and the front and rear surface centers of the suspension shaft are uniformly provided with a plurality of horizontally oriented suspension air nozzles along the axial direction; The right end of the suspension shaft is an opening, and the right end portion thereof can be placed on an arc-shaped limiting plate fixed to the right inner wall of the heat treatment equipment shell;

[0016] Telescopic rotary drive system: including a telescopic rod that can be telescoped left and right on the right side wall of the heat treatment equipment shell, a magnetic head fixed to the left end of the telescopic rod and extendable into the right end opening of the suspension shaft, a driven conical gear assembled on the right end of the telescopic rod through a spline, a motor installed on the right side wall of the heat treatment equipment shell, and a driving conical gear fixed to the output end of the motor and engaged with the driven conical gear; The magnetic head is composed of a magnetic block and heat insulation blocks encapsulated at both ends thereof;

[0017] Cooling and gas source pretreatment system: including a heat exchange frame installed on the left side wall of the heat treatment equipment shell, and a heat exchange coil pipe coiled in the heat exchange frame; One end of the heat exchange coil pipe is connected to the left end of the rotating sleeve through a rotary joint, and the other end is externally connected to a high-pressure nitrogen gas source; The heat exchange frame is provided with a cooling water inlet and outlet;

[0018] The suspension air nozzles, the inner cavity of the suspension shaft, the inner cavity of the rotating sleeve, and the heat exchange coil pipe are sequentially communicated to form an airflow passage.

[0019] Further, the outer diameter of the suspension shaft is smaller than the inner diameter of the metal pipe to be treated, and there is a concentric annular gap between them.

[0020] Further, the curvature radius of the groove of the arc-shaped limiting plate matches the outer diameter of the right end of the suspension shaft, for radial limiting and auxiliary support.

[0021] Further, the heat insulation block in the magnetic head is made of high-temperature-resistant heat insulation material, such as ceramic fiber or aerogel.

[0022] Further, the device further comprises a control system for controlling the start-stop and rotating speed of the motor, the extension and retraction of the telescopic rod, the heating power of the electric heating guide wire, and the on-off and flow of the nitrogen source and cooling water.

[0023] A method for heat treatment of metal surface using the above device, characterized in that it comprises the following steps:

[0024] S1. Loading: rotate the suspension shaft out of the heat treatment equipment shell, put the metal pipe on the suspension shaft, and then rotate the assembly back into the heat treatment equipment shell, so that the right end of the suspension shaft falls on the arc-shaped limiting plate;

[0025] S2. Start air floating and heating: turn on the nitrogen source and cooling water, and low-temperature high-pressure nitrogen gas enters the suspension shaft after being cooled by the heat exchange coil, and is sprayed out of the suspension gas nozzle to support the metal pipe in suspension; at the same time, turn on the electric heating guide wire to heat the metal pipe;

[0026] S3. Drive rotation: push the telescopic rod to the left to make the magnetic head extend into the right end of the suspension shaft and approach the metal pipe; start the motor to drive the magnetic head to rotate, which drives the metal pipe to rotate synchronously through magnetic coupling;

[0027] S4. Implement heat-cold cycle: during heating and rotation, continuously pass in low-temperature nitrogen gas to cause instantaneous cooling of the inner wall of the metal pipe under the action of low-temperature gas flow, while the outer wall is continuously heated by the electric heating guide wire, and through the adjustment of process parameters, multiple rapid austenite-martensite phase change cycles are induced in the thickness direction of the metal pipe wall;

[0028] S5. Cooling and unloading: after the process is completed, stop heating, continue to pass nitrogen gas to cool to a safe temperature, then stop all power, withdraw the magnetic head, and rotate out and remove the metal pipe.

[0029] Further, in step S2, the temperature of the low-temperature nitrogen gas is controlled below 50°C by the heat exchange system.

[0030] Further, in step S2, the minimum air floating pressure required to suspend the metal pipe is which needs to overcome the gravity of the metal pipe, which satisfies:

[0031]

[0032] where m is the mass of the metal pipe, g is the acceleration of gravity, Effective bearing area of the gas film, actual operating pressure 1.5 to 3 times to ensure stability.

[0033] Further, in step S3, the rotation speed ω of the metal tube is selected according to the size of the metal tube and the requirements of the heat treatment process, and the range is usually between 5 and 50 RPM.

[0034] Further, step S4 is the key to improve the performance of the present application, which is to achieve controllable cyclic phase change in the near-surface region of the metal tube by controlling the temperature , flow , heating power of nitrogen. The cooling rate of each cooling process is a key parameter, which approximately satisfies:

[0035]

[0036] Where, and are the density and specific heat capacity of nitrogen at constant pressure, respectively, is the temperature of the inner wall of the metal tube, is the effective mass involved in heat exchange. By controlling to be higher than the critical cooling rate of martensitic transformation of the material, the phase change can be realized.

[0037] Compared with the prior art, the present application provides a metal surface heat treatment device and a processing method, which has the following beneficial effects:

[0038] 1. The gas suspension technology is used to support the metal tube, which completely avoids the damage, deformation and coating damage caused by mechanical clamping, and is especially suitable for the treatment of precision workpieces.

[0039] 2. The supporting force of the gas suspension is derived from the gas dynamics effect, and its performance does not decay with the increase of environmental temperature, which fundamentally solves the world-wide problem of magnetic suspension high-temperature demagnetization, and has very high reliability.

[0040] 3. By driving the suspended metal tube to rotate at a constant speed, combined with the heating of the surrounding electric heating wire, the heating temperature of the metal tube in the circumferential and axial directions is highly uniform, and the heat treatment soft point and uneven structure are effectively eliminated.

[0041] 4. The cooling gas flow is innovatively combined with the heat treatment process to realize "heat-cold cycle" through precise control, which can actively induce multiple fine-grain strengthening and phase change strengthening of the material structure, significantly improve the hardness, strength and wear resistance of the metal tube surface, and break through the limitation of traditional heat treatment which can only rely on the characteristics of the material itself.

[0042] 5. The continuously supplied low-temperature nitrogen gas not only serves as the process gas, but also forcibly cools the internal mechanisms such as the magnetic head and the rotating sleeve, ensuring long-term reliable operation of the driving system in a high-temperature environment and prolonging the service life of the equipment.

[0043] 6. The device and method are suitable for high-quality surface heat treatment of various tubular and shaft metal parts in an atmospheric environment, and the process is flexible and easy to integrate into an automatic production line. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Fig. 1 is a perspective view of the suspension shaft rotating out of the heat treatment equipment shell according to the present application;

[0045] Figure 2 Fig. 2 is a perspective view of the suspension shaft rotating into the heat treatment equipment shell according to the present application;

[0046] Figure 3 Fig. 3 is a perspective view of the installation structure of the telescopic assembly on the side wall of the heat treatment equipment shell according to the present application;

[0047] Figure 4 Fig. 4 is a perspective view of the installation structure of the heat exchange frame on the side wall of the heat treatment equipment shell according to the present application;

[0048] Figure 5 Fig. 5 is a perspective view of the installation structure of the suspension shaft according to the present application;

[0049] Figure 6 Fig. 6 is a perspective view of the telescopic assembly according to the present application;

[0050] Figure 7 Fig. 7 is a structural view of the magnetic head according to the present application;

[0051] Figure 8 Fig. 8 is a structural view of the heat exchange coil according to the present application.

[0052] In the drawings: 1, telescopic assembly; 2, electric heating guide wire; 3, heat treatment equipment shell; 4, metal pipe suspension assembly; 5, metal pipe; 6, suspension shaft; 7, rotating sleeve; 8, magnetic block; 9, vertical shaft; 10, heat insulation block; 11, water inlet; 12, heat exchange frame; 13, heat exchange coil; 14, water outlet; 15, suspension gas jet; 16, arc-shaped limiting plate; 17, magnetic head; 18, telescopic rod; 19, motor; 20, driven conical gear; 21, driving conical gear. DETAILED DESCRIPTION

[0053] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0054] Embodiment 1

[0055] Please refer to Figures 1 to 8 The present embodiment provides a metal surface heat treatment device and a treatment method. The core design concept of the device is to solve the three major pain points in the surface heat treatment of traditional pipe and shaft parts: first, uneven heating, coating damage and deformation caused by mechanical clamping; second, uneven static heating of the workpiece during heat treatment, affecting the consistency of the structure transformation; and third, the problem of failure of the existing non-contact suspension scheme at high temperature due to loss of magnetic material. The present application skillfully integrates air suspension, rotary drive and active cooling technology, realizes stable, non-contact and uniform treatment of the workpiece in a high temperature environment, and can improve the final performance through a unique "heat-cold cycle" process.

[0056] The device body is a heat treatment equipment shell 3, and an electric heating guide wire 2 for heating is installed on the inner wall of the heat treatment equipment shell 3. The heat treatment equipment shell 3 constitutes a closed or semi-closed heat treatment chamber, providing a high-temperature environment for heat treatment and reducing heat loss.

[0057] The core movement and support mechanism of the device includes:

[0058] Vertical shaft 9: fixedly installed on the inner left side wall of the heat treatment equipment shell 3, serving as the static support basis of the entire rotating mechanism.

[0059] Rotary sleeve 7: sleeved on the vertical shaft 9 through a bearing or other rotating mechanism, and can freely rotate around the vertical shaft 9. The right end is open, used for connecting the external air source with the internal suspension air supply system.

[0060] Metal pipe suspension assembly 4: its core is a hollow suspension shaft 6, the left end of which is fixedly connected with the rotary sleeve 7 and communicates with the inside of the rotary sleeve 7. The top, front and rear surfaces of the suspension shaft 6 are evenly distributed with a plurality of suspension air nozzles 15 in the axial direction. The directions of these nozzles are precisely designed to be horizontally outward. The right end of the suspension shaft 6 is open. When working, the metal pipe 5 to be treated is sleeved on the outside of the suspension shaft 6.

[0061] The right side of the device is provided with an extension assembly 1, which is used to drive the metal pipe 5 to rotate and protect the driving magnet. It includes:

[0062] Telescopic rod 18: Its left end extends into the heat treatment equipment shell 3, and the right end extends out of the heat treatment equipment shell 3. Its left end is fixedly connected with the magnetic head 17.

[0063] Magnetic head 17: It is the key component for driving the metal pipe 5 to rotate, which is composed of a central magnetic block 8, preferably a high magnetic energy product and high Curie temperature permanent magnet such as neodymium iron boron, and heat insulation blocks 10 encapsulated at both ends. The heat insulation blocks 10 can be made of high-performance heat insulation materials such as ceramics and aerogels. The heat insulation blocks 10 block the transfer of high temperature to the magnetic block 8.

[0064] Driving mechanism: composed of motor 19, driving bevel gear 21 and driven bevel gear 20. The driven bevel gear 20 is connected with the telescopic rod 18 through spline, so that it can not only transmit torque, but also allow the telescopic rod 18 to move axially. The motor 19 drives the driving bevel gear 21, thereby driving the driven bevel gear 20 and the telescopic rod 18 to rotate.

[0065] The device also contains a delicate cooling and gas source pretreatment system:

[0066] Arc-shaped limiting plate 16: fixed to the inner right side wall of the heat treatment equipment shell 3. When the suspension shaft 6 rotates into the working position, its right end is placed in the arc-shaped groove, achieving precise positioning and auxiliary support.

[0067] Heat exchange frame 12: installed on the left side wall of the heat treatment equipment shell 3. It is provided with water inlet 11 and water outlet 14 for circulating cooling water.

[0068] Heat exchange coil 13: coiled and installed inside the heat exchange frame 12. One end is connected with the left end of the rotating sleeve 7 through a rotary joint (not shown in the figure, but common technology in the field), and the other end is externally connected with a high-pressure nitrogen source. Its function is to use flowing cooling water to forcibly cool the high-pressure nitrogen gas about to be introduced into the suspension shaft 6.

[0069] The working principle and processing process of the present application are as follows:

[0070] Step one: loading

[0071] In the initial state, the telescopic assembly 1 is retracted, and the magnetic head 17 is located outside the heat treatment equipment shell 3.

[0072] The operator or mechanical hand rotates the entire suspension shaft 6 out of the heat treatment equipment shell 3 through the rotating sleeve 7.

[0073] The metal pipe 5 to be processed is carefully sleeved outside the suspension shaft 6.

[0074] The suspension shaft 6 with the metal pipe 5 sleeved is rotated back into the heat treatment equipment shell 3 until the right end of the suspension shaft 6 is stably placed on the arc-shaped limiting plate 16, completing the precise positioning.

[0075] Step two: start gas suspension and heating

[0076] Start the external high-pressure nitrogen source and cooling water circulation system.

[0077] High-pressure normal-temperature nitrogen gas is introduced into the heat exchange coil 13, and low-temperature cooling water is pumped into the heat exchange frame 12 from the water inlet 11 and flows out from the water outlet 14. In the heat exchange coil, the coolant and the heat medium exchange heat through the coil wall in countercurrent. The temperature of the nitrogen gas after heat exchange is greatly reduced, becoming low-temperature nitrogen gas.

[0078] This low-temperature high-pressure nitrogen gas flows through the rotating sleeve 7, enters the hollow cavity of the suspension shaft 6, and finally is sprayed out at high speed from the uniformly distributed suspension gas nozzles 15.

[0079] According to the principle of fluid mechanics, the high-speed sprayed gas forms a stable gas film in the narrow gap between the suspension shaft 6 and the inner wall of the metal pipe 5, generating enough pressure to completely lift the metal pipe 5, achieving non-contact gas suspension. The minimum gas floating pressure required To overcome the gravity of the metal pipe 5, the calculation formula can be simplified as:

[0080]

[0081] Where m is the mass of the metal pipe 5, g is the acceleration of gravity, is the effective bearing area of the gas film, which is related to the number and layout of the nozzles and the gap. The actual operating pressure must be much greater than to ensure stability.

[0082] At the same time, the electric heating wire 2 is energized to generate heat, and the metal pipe 5 in the suspended state is radiated and heated, so that the surface temperature of the metal pipe 5 rapidly rises to the predetermined austenitizing temperature.

[0083] Step three: drive rotation and homogenization treatment

[0084] After the surface temperature of the metal pipe 5 reaches the set value and remains for a certain period of time, the telescopic assembly 1 is started. The telescopic rod 18 is pushed to the left, so that the magnetic head 17 at the end of the telescopic rod 18 extends into the right end opening of the suspension shaft 6 and is as close as possible to the right end of the metal pipe 5.

[0085] Start the motor 19, and the motor 19 transmits power to the telescopic rod 18 through the engagement of the driving bevel gear 21 and the driven bevel gear 20, and then drives the magnetic head 17 to rotate at high speed.

[0086] The rotating magnetic head 17 penetrates the air gap and possible small spaces through strong magnetic coupling, driving the metal pipe 5 in the suspended state to rotate around the axis of the suspension shaft 6.

[0087] The uniform rotation of the metal tube 5, combined with the surrounding heating of the electrically heated wire 2, ensures that the heat treatment temperature of the metal tube 5 is extremely uniform in the circumferential and axial directions, laying a solid foundation for subsequent microstructure transformation. The selection of the rotation speed ω (rad / s) needs to avoid causing severe fluctuations in the airflow field, and the upper limit can be estimated by the critical Reynolds number.

[0088] Step four: Implementing the hot-cold cycle process

[0089] This is the key to improving the performance of the invention. While heating and rotating, continuously pass in the pre-cooled low-temperature nitrogen.

[0090] Instant cooling effect: The low-temperature nitrogen gas sprayed from the suspension gas nozzle 15 will instantly take away the heat of the inner wall of the metal tube 5 in contact with it while lifting the metal tube 5. For a metal tube 5 heated to 800°C, the inner wall will experience rapid local cooling.

[0091] Continuous heating effect: At the same time, the external electrically heated wire 2 continuously radiates heat to the outer wall of the metal tube 5, which conducts heat from the outside to the inside.

[0092] Dynamic balance and cyclic phase change: This forms an interesting "tug-of-war": the outer wall is heated, and the inner wall is cooled. In the thickness direction of the metal tube 5, a dynamic temperature field will be formed. By precisely controlling the nitrogen temperature ( ), flow ( ), heating power ( ) and process time ( ), multiple rapid austenite-martensite phase change cycles can be induced in the interior of the metal tube 5, especially in the near-surface region.

[0093] Cooling rate of each cycle The cooling rate of each cycle can be estimated by the nitrogen heat exchange efficiency:

[0094]

[0095] where, and are the density and specific heat capacity of nitrogen, is the inner wall temperature of the metal tube 5, is the effective mass involved in heat exchange.

[0096] This process is similar to multiple ultra-short-time surface quenching, which can significantly refine the grains and increase the dislocation density, thereby greatly improving the surface hardness, strength and wear resistance without sacrificing toughness. It achieves better microstructure and performance through multiple controllable phase changes.

[0097] Step five: Cooling and unloading

[0098] After the heat treatment process is completed, first stop the electrically heated wire 2 heating.

[0099] Continue to pass low-temperature nitrogen to perform final overall cooling of the metal tube 5 until a safe temperature.

[0100] Stop the motor 19 and stop the nitrogen and cooling water supply.

[0101] Retract the telescopic assembly 1 to withdraw the magnetic head 17.

[0102] Rotate out the suspension shaft 6 together with the metal tube 5 that has completed processing, and remove the metal tube 5.

[0103] Self-protection mechanism of the device:

[0104] Throughout the process, the low-temperature nitrogen that is passed also undertakes a crucial cooling task:

[0105] Cooling the magnet: the low-temperature nitrogen flowing through the inside of the suspension shaft 6 continuously takes away heat around the magnetic head 17, forcibly air-cools the heat insulation block 10 and the magnetic block 8, and ensures that their temperature is always far below the Curie temperature of the magnet, thereby avoiding the risk of high-temperature demagnetization.

[0106] Cooling mechanism: the low-temperature gas flow also ensures that the internal mechanisms such as the rotating sleeve 7 and the suspension shaft 6 do not overheat and get damaged due to radiation heat, thereby improving the reliability and service life of the device.

[0107] Experimental example

[0108] To verify the superiority of the device and the processing method, we conducted a comparative experiment using a 45 steel tube as an example.

[0109] Experimental conditions:

[0110] Metal tube 5: φ50mm x 500mm 45 steel tube, wall thickness 5mm.

[0111] Control group: traditional box-type resistance furnace heating and oil quenching.

[0112] Experimental group: use the device for processing. Heat to 840°C and keep for 5 minutes. Pass in nitrogen at a pressure of 1.0MPa and a temperature of 25°C after cooling, with a flow rate of 50L / min and a metal tube 5 rotation speed of 20RPM. Perform 3 cycles of "heating-cooling" cycles, with a total processing time of 15 minutes.

[0113] Detection: after processing, take 4 points to measure hardness (HRC) on the same circumference in the middle of the metal tube 5, and cut metallographic samples to observe the microstructure.

[0114] The experimental results are shown in Table 1 below:

[0115] Table 1

[0116]

[0117] Experimental conclusion:

[0118] Performance improvement: The surface hardness of the experimental group metal pipe 5 is significantly higher than that of the traditional method, which benefits from the fine-grain strengthening and dislocation strengthening generated by cyclic phase change.

[0119] Excellent uniformity: Both the hardness data and the microstructure of the experimental group show excellent uniformity, which proves the superiority of gas suspension rotary heating and completely eliminates the cold spots and static heating of clamping.

[0120] No damage: The metal pipe 5 is in a non-contact state throughout the entire processing process, and the surface pretreatment coating is intact without any clamping deformation.

[0121] High reliability: During the entire experimental process, the magnetic suspension driving system works normally without any loss of magnetism, which proves the effectiveness of the integrated cooling system.

[0122] In summary, the metal surface heat treatment device and processing method provided by the present application successfully integrates non-contact support, uniform rotary heating, active cooling protection and innovative thermal cycle process, effectively solves many drawbacks in traditional heat treatment, significantly improves the processing quality and comprehensive performance of the metal pipe 5, and has extremely high industrial application value.

Claims

1. A metal surface heat treatment apparatus, comprising a heat treatment equipment shell (3) and an electric heating wire (2) installed on its inner sidewall, characterized in that: It also includes, The air suspension rotation support system includes a vertical shaft (9) fixedly installed on the inner left side wall of the heat treatment equipment shell (3), a rotating sleeve (7) rotatably fitted on the vertical shaft (9), and a hollow suspension shaft (6) fixedly connected to the rotating sleeve (7). The outer surface of the suspension shaft (6) has several horizontally arranged suspension air nozzles (15) evenly distributed along the axial direction. The right end of the suspension shaft (6) is an opening. The telescopic rotation drive system includes a telescopic rod (18) that can be telescopically mounted on the right side wall of the heat treatment equipment housing (3), a magnetic head (17) fixed to the left end of the telescopic rod (18) and extending into the right end opening of the suspension shaft (6), a driven bevel gear (20) mounted on the telescopic rod (18) via a spline, a motor (19) mounted on the right side wall of the heat treatment equipment housing (3), and an active bevel gear (21) fixed to the output end of the motor (19) and meshing with the driven bevel gear (20). The cooling and air source pretreatment system includes a heat exchange frame (12) installed on the left side wall of the heat treatment equipment shell (3) and a heat exchange coil (13) coiled inside the heat exchange frame (12). One end of the heat exchange coil (13) is connected to the rotating sleeve (7), and the other end is used to connect to an external high-pressure air source. The heat exchange frame (12) is provided with a cooling water inlet (11) and an outlet (14).

2. The metal surface heat treatment apparatus according to claim 1, characterized in that: The suspension air nozzle (15) is provided at the top and the center of the front and rear sides of the suspension shaft (6).

3. The metal surface heat treatment apparatus according to claim 1, characterized in that: An arc-shaped limiting plate (16) is fixedly installed on the inner right side wall of the heat treatment equipment shell (3), and the right end of the suspension shaft (6) can be placed on the arc-shaped limiting plate (16).

4. The metal surface heat treatment apparatus according to claim 1, characterized in that: The magnetic head (17) is composed of a magnetic block (8) and heat insulation blocks (10) fixedly encapsulated at both ends.

5. The metal surface heat treatment apparatus according to claim 4, characterized in that: The heat insulation block (10) is made of ceramic or aerogel material.

6. The metal surface heat treatment apparatus according to claim 1, characterized in that: The suspended air nozzle (15), the inner cavity of the suspended shaft (6), the inner cavity of the rotating sleeve (7), and the heat exchange coil (13) are connected in sequence to form an airflow passage.

7. The metal surface heat treatment apparatus according to any one of claims 1 to 6, characterized in that: It also includes a control system, which is electrically connected to the motor (19) and the heating wire (2), and is used to control the on / off state and flow rate of the air source connected to the heat exchange coil (13) and the cooling water source connected to the water inlet (11).

8. A method for heat treatment of metal surfaces, used in the metal surface heat treatment apparatus according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Unscrew the suspension shaft (6) out of the heat treatment equipment housing (3), put the metal tube (5) over the suspension shaft (6), and then screw the assembly back so that the right end of the suspension shaft (6) falls onto the arc-shaped limiting plate (16); S2. High-pressure gas is introduced into the heat exchange coil (13) and cooling water is introduced into the heat exchange frame (12). The cooled gas enters the suspension shaft (6) through the rotating sleeve (7) and is ejected from the suspension gas nozzle (15) to suspend the metal tube (5). At the same time, the electric heating wire (2) is turned on to heat the metal tube (5). S3. Push the telescopic rod (18) to the left so that the magnetic head (17) extends into the right end of the suspension shaft (6); start the motor (19) to drive the magnetic head (17) to rotate, and drive the metal tube (5) to rotate through magnetic coupling; S4. During the heating and rotation process, the cooled gas is continuously introduced so that the inner wall of the metal tube (5) is cooled while the outer wall is continuously heated. By controlling the process parameters, multiple austenitic-martensite phase transformation cycles are induced in the wall thickness direction of the metal tube (5). S5. Stop heating, continue to introduce cooling gas to cool the metal tube (5) to a safe temperature, then stop all power, remove the magnetic head (17), and unscrew and remove the metal tube (5).

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